Subtraction consists in shortening the shape of the word. It operates on morphological bases such as roots, stems, and words in word-formation and inflection. Cognitively, subtraction is the opposite of affixation, since the latter adds meaning and form (an overt affix) to roots, stems, or words, while the former adds meaning through subtraction of form. As subtraction and affixation work at the same level of grammar (morphology), they sometimes compete for the expression of the same semantics in the same language, for example, the pattern ‘science—scientist’ in German has derivations such as Physik ‘physics’—Physik-er ‘physicist’ and Astronom-ie ‘astronomy’—Astronom ‘astronomer’. Subtraction can delete phonemes and morphemes. In case of phoneme deletion, it is usually the final phoneme of a morphological base that is deleted and sometimes that phoneme can coincide with a morpheme. Some analyses of subtraction(-like shortenings) rely not on morphological units (roots, stems, morphological words, affixes) but on the phonological word, which sometimes results in alternative definitions of subtraction. Additionally, syntax-based theories of morphology that do not recognize a morphological component of grammar and operate only with additive syntactic rules claim that subtraction actually consists in addition of defective phonological material that causes adjustments in phonology and leads to deletion of form on the surface. Other scholars postulate subtraction only if the deleted material does not coincide with an existing morpheme elsewhere in the language and if it does, they call the change backformation. There is also some controversy regarding what is a proper word-formation process and whether what is derived by subtraction is true word-formation or just marginal or extragrammatical morphology; that is, the question is whether shortenings such as hypocoristics and clippings should be treated on par with derivations such as, for example, the pattern of science-scientist. Finally, research in subtraction also faces terminology issues in the sense that in the literature different labels have been used to refer to subtraction(-like) formations: minus feature, minus formation, disfixation, subtractive morph, (subtractive) truncation, backformation, or just shortening.